//: C08:Volatile.cpp
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 1999
// Copyright notice in Copyright.txt
// The volatile keyword

class Comm
{
    const volatile unsigned char byte;
    volatile unsigned char flag;
    static const int bufsize = 100;
    unsigned char buf[bufsize];
    int index;
public:
    Comm();
    void isr() volatile;
    char read(int index) const;
};

Comm::Comm() : index(0), byte(0), flag(0) {}

// Only a demo; won't actually work
// as an interrupt service routine:
void Comm::isr() volatile {
    if (flag) flag = 0;
    buf[index++] = byte;
    // Wrap to beginning of buffer:
    if (index >= bufsize) index = 0;
}

char Comm::read(int index) const
{
    if (index < 0 || index >= bufsize)
        return 0;
    return buf[index];
}

int main()
{
    volatile Comm Port;
    Port.isr(); // OK
//!  Port.read(0); // Error, read() not volatile
} ///:~
